A protective cover assembly, as disclosed in Chinese Patent Publication No. CN105980925, includes a protective cover having a through hole, and a retainer clamped to an outer portion of the protective cover for fixing an accessory unit to the latter. Since the retainer and the accessory unit are both disposed on the outer portion of the protective cover, their chance of being hit and falling is increased. Further, because the retainer is simply clamped to the protective cover, when impacted by an external force, the retainer together with the accessory unit may fall off from the protective cover. Moreover, since the size of the opening matches with that of the retainer, and since the retainer must have a large surface area in order to stably clamp to the protective cover, when the accessory unit is not in use, the protective cover will present a rather large opening, thereby adversely affecting an appearance thereof.